It is known that coordination catalyst systems (Ziegler-Natta type catalysts) may be employed for polymerizing conjugated dienes into cis 1,4-polydienes, for example, polymerizing 1,3-butadiene to form cis-1,4-polybutadiene. Such coordination catalyst systems may be based on transition metals such as titanium, cobalt and nickel, or lanthanide metals such as neodymium.
The cis 1,4-polydienes produced by coordination catalyst systems can have a broad molecular weight distribution. Because a polymer having a narrower molecular weight distribution may offer certain advantages such as higher abrasion resistance, lower hysteresis, and better tensile properties, it is desirable to develop a coordination catalyst system that is capable of producing cis 1,4-polydienes having a narrower molecular weight distribution.
Commonly owned U.S. patent application Ser. No. 12/270,424, filed Nov. 13, 2008, discloses a nickel-based catalyst composition comprising (a) a nickel N-heterocyclic carbene complex, (b) an organoaluminum compound, (c) a fluorine-containing compound, and (d) optionally, an alcohol. The catalyst composition can produce cis 1,4-polydienes, for example, high cis 1,4-polybutadiene with a narrow molecular weight distribution and a low vinyl content. However, the nickel N-heterocyclic carbene complex must be prepared before adding it to the catalyst composition. A need still remains for a catalyst composition that does not require a carbene complex to be prepared outside of (i.e. prior to preparation of) the catalyst composition.
“Vinyl content” is used herein to refer to the amount of pendant vinyl groups on the polymer chain, which result from 1,2-addition rather than 1,4-addition.
“Transition metals” are those that are in groups 3-12 in the IUPAC version of the periodic table.
“Lanthanide metals” are elements 57-71 on the periodic table.